1. Technical Field
Embodiments of the invention relate to a semiconductor manufacturing apparatus. More particularly, embodiments of the invention relate to a Faraday system adapted to determine the concentration of an ion beam irradiated onto a wafer, and an ion implantation apparatus using the Faraday system.
This application claims priority to Korean Patent Application No. 10-2005-0088151, filed Sep. 22, 2005, the subject matter of which is hereby incorporated by reference in its entirety.
2. Discussion of Related Art
Contemporary semiconductor devices are characterized by increasing integration density, reduced overall size, and improved performance. These results are achieved through careful improvements in the complex sequence of fabrication processes used to make semiconductor devices. One of these fabrication processes generally involves the implantation of conductive impurity ions into a silicon wafer.
Ion implantation is a basic fabrication process through which impurities are selectively introduced into a semiconductor substrate. Many times, an ion implantation process is performed in conjunction with a thermal diffusion process. Despite its long history of use in the fabrication of semiconductor devices, the small size and increasingly strict manufacturing tolerances associated with contemporary semiconductor devices have generated a greater emphasis on the precise control of ion implantation processes. Further, from a mass production perspective, relatively precise control over implanted impurity concentrations is required to improve reproducibility of semiconductor devices.
There are a variety of ion implantation apparatuses in which a precise ion implantation process may be performed. A conventional ion implantation apparatus comprises an ion source adapted to produce conductive impurity ions, a mass analyzer adapted to the separation and extraction of the impurity ions, a magnetic collector adapted to collect separated/extracted impurity ions, and a scanning system adapted to output an ion beam of defined beam width comprising the collected impurity ions. The conventional ion implantation apparatus further comprises an accelerator adapted to accelerate the ion beam output by the scanning system, a target adapted to hold (i.e., fix) a wafer and move the wafer in at least one dimension, and a Faraday system disposed adjacent to the target and adapted to determine the concentration (i.e., dose) of the ion beam.
The Faraday system may precisely determine the concentration at which the ion beam implants impurity ions into the wafer so that the ion implantation apparatus can prevent impurity ions from being implanted with a concentration that is too high or too low. Accordingly, the Faraday system is disposed adjacent to, but separated from the target holding the wafer, so that the Faraday system may collect an edge portion of the ion beam being irradiated on the wafer to thereby count the concentration of impurity ions in the ion beam.
Exemplary, conventional Faraday systems are disclosed in U.S. Pat. Nos. 4,922,106, 4,980,562, and 6,723,988, the subject matter of which is hereby incorporated by reference.
Hereinafter, a conventional Faraday system will be described with reference to Figure (FIG.) 1 which is a cross-sectional schematic view.
As shown in FIG. 1, a conventional Faraday system 10 comprises a Faraday cup 12 adapted to collect an ion beam 20 and generate a corresponding current. Faraday system 10 further comprises a suppression electrode 14 adapted to form an electric field of defined magnitude adjacent to an inlet of Faraday cup 12 in order to prevent secondary electrons collected in Faraday cup 12 from being discharging in response to ion beam 20. Faraday system 10 still further comprises a housing 16 surrounding suppression electrode 14 and Faraday cup 12 and having an aperture 15 through which ion beam 20 may pass and enter Faraday cup 12.
Faraday cup 12 is a bowl-shaped metal structure. Assuming ion beam 20 comprises a plurality of conductive impurity ions having a positive charge, for example, a flow of electrons (i.e., electric current) will be induced in Faraday cup 12 in response to the impact of ion beam 20. This current may be detected by an ammeter 17 connected in series between Faraday cup 12 and ground 19.
Suppression electrode 14 surrounding the opening of Faraday cup 12 may be connected to an external voltage supply element 18 in order to form the requisite electric field. The electric field prevents ion beam 20 from colliding with the outer surface of Faraday cup 12, and thereby impedes the generation of, accumulation on, and discharge of secondary electrons in relation to Faraday cup 12.
In addition, housing 16 shields the outer surface of Faraday cup 12 from ion beam 20 while allowing ion beam 20 to pass into Faraday cup 12 through aperture 15 formed in housing 16. Housing 16 is connected to ground 19 such that an electric charge potential is developed on housing 16 by ion beam 20. The size of aperture 15 defines the portion of ion beam 20 provided into Faraday cup 12.
As illustrated in FIG. 1, a first face of housing 16 is oriented to be perpendicular to the direction of ion beam 20. Aperture 15 is commonly a rectangular shape and is disposed in the center of the first face of housing 16.
However, within this system configuration, impurity ions of first conductivity type may nonetheless collect on the first face of housing 16 in areas proximate aperture 15. Thereafter, when an impurity ions of second conductivity type are subsequently applied through aperture 15 of housing 16, the impurity ions of the first conductivity type collected on the first face of housing 16 may be picked-up by the ion beam 20 communicating the subsequently applied second conductivity type impurity ions, and thereby contaminate the surface of the wafer being processed in Faraday system 10. Such contamination reduces production yield of the semiconductor devices formed on the wafer.